Poromeric material and method of making same



POROMERIG MATERIAL AND METHOD OF MAKING SAME Filed April 12, 1963 DISPERSION OF FIBERS IN SOLUTION OF POLYMERIC MATERIAL APPLY DISPERSION TO A NONWOVEN FABRIC.

NOIIWOVEN FABRIC COATED WITH LAYER OF DISPERSION BATHE WITH MIXTURE OF SOLVENT AND NONSOLVENT (FOR POLYMER).

NONWOVEN FABRIC WITH FIBER CONTAINING MICROPOROUS POLYMERIC COATING REMOVE SOLVENT AND REMOVE NONSOLVENT.

DRY NONWOVEN FABRIC WITH FIBER-CONTAINING MICROPOROUS POLYMERIC COATING PRESS TO INCREASE COATING DENSITY TO AT LEAST 0.4 GRAMS/CC.

IIONWOVEII FABRIC WITH NON- ROUGHENINC MICROPOROUS COATING INVENTOR EDGAR F! BRIGHTWELL ATTORNEY United States Patent C 3,238,055 PUROMERIC MATERIAL AND METHUD F MAKENG SAME Edgar P. Brightwell, Wilmington, Del., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del,

a corporation of Delaware Filed Apr. 12, 1963, Ser. No. 272,549 14 Claims. (Cl. 11765.2)

such a product is taught, for example, in U.S. Patent 3,000,757, Example 5. Woven fabrics are not commonly used when smoothness is important because the weave pattern of the fabric tends to show through the microporous coating unless the coating thickness is increased to a point where other problems are introduced, such as excessive cost and nonleatherlike flex-and-fold properties.

The more durable grades of these poromeric products are made with a relatively dense, yet porous, fiber-interlocked fabric, the fiber interlocking being accomplished by needle-punching, hot-pressing and/or by incorporating a porous polymeric binder. Unfortunately, the nonwoven fabrics of this type which provide the best combination of durability and vapor permeability, when coated with the microporous polymeric layer at optimum thickness, often do not provide the degree of surface smoothness desired in certain products, particularly when the material is under tension. For example, in smoothfini-sh types of shoe-uppers and upholstery products, the surface tends to appear rough in areas of the product applied under tension, for example, on the toe areas of shoes and along the edges of upholstered articles. In such areas the material is often applied under sufiicient tension to stretch it (to increase its length and/or width).

It is therefore an object of this invention to provide a poromeric sheet material of the type discussed above having improved surface smoothness when under tension, especially when stretched beyond its original area dimensions. It is also an object to provide a method of making the new and improved poromeric product. Other objects will be apparent from the description of the invention which follows A simplified flow diagram of the method of this invention is illustrated by the drawing.

Expressed broadly, the product of this invention is a new and improved poromeric sheet material comprising Layers A and B as follows:

(A) a vapor permeable nonwoven fabric in which the fibers are in entangled and interlocked relationship with one another, and

(B) in superposed adherence with Layer A, a microporous vapor-permeable layer of flexible polymeric material in which the pores are inter-communicating;

Layer B has a density of at least 0.4 gram per cubic centimeter, and contains randomly dispersed staple fibers, a majority of which are free of direct contact with one another; the weight ratio of the polymeric material to the dispersed fibers therein being about 80:20 to 97:3.

A preferred nonwoven fabric for use as Layer A is in the form of a ligated fibrous mat maintaining in situretracted organic fibers, said mat having been shrunk 3,238,055 Patented Mar. 1, 1966 about 10 to 90% of its original planar area, and dispersed throughout said mat about 5 to 90% of a porous flexible polymeric impregnant based on the combined weight of fibers and impregnant.

Ligated means that adjacently disposed fibers lying substantially parallel to the surface of the mat are bound together as the result of enough of the fibers having been forcibly oriented to a position substantially perpendicular to the surface of the mat to form a unitary, dense, coherent structure. Ligation is preferably accomplish-ed by punching the mat with fine needles mounted in a conventional needle-loom, for example, rasping profile needles or barbed needles.

The product of this invention as broadly defined above can be made by a novel method which comprises (1) applying to the nonwoven fabric (Layer A described above) a layer of a dispersion of flexible polymeric material and staple fibers in a liquid which is a solvent for the polymer and a non-solvent for the fibers, the weight ratio of said polymeric material to said fibers being about :20 to 97:3.

(2) coagulating the layer applied in (1) into an intercomrnunicating microporous structure by bathing it with a liquid non-solvent for the polymer that is at least partially miscible with the liquid used in (l),

(3) removing substantially all of the solvent from the microporous layer, I

(4) removing substantially all of the non-solvent from the resulting solvent-free microporous layer, and

(5) pressing the resulting composite structure under conditions sufficient to increase the density of the coating permanently to at least 0.4 gram per cubic centimeter, but not sufiicient to render the coating nonporous.

The novel product unexpectedly has superior smoothness when under tension compared with products made in the same manner except for omission of the staple fibers in step (1).

The methor of this invention is adaptable to the rapid and economical production of new and improved vapor permeable, flexible, smooth-surface, poromeric sheet materials. Consistent yields of uniformly high quality products of this type are readily obtainable.

When making Layer B from such preferred polymers as polyurethane elastomers or blends thereof with polyvinyl chloride, and such preferred staple fibers as nylon or poly(ethylene terephthalate), step 5 is preferably carried out by pressing the structure for about 60 to seconds at a platen or nip temperature of about to C. and at a pressure of about 5 to 20 p.s.i.g. (pounds per square inch gauge).

The preferred ligated nonwoven fabric described above can be made in accordance with the disclosure of U.S. Patent 3,067,483, which disclosure is incorporated herein by reference.

Other nonwoven fabrics which are vapor permeable and in which the fibers are entangled and interlocked are also useful as Layer A. The fibers can be interlocked by any known method, for example, by incorporating a polymeric binder during or after mat formation, by needlepunching, and/or by activating the self-bonding characteristic of the thermoplastic fibers by means of heat, pressure and/or a solvent. The fibers of Layer A can be natural or synthetic, crirnped or straight, organic or inorganic, continuous filament or staple, or of papermaking length. In the embodiments of the invention having the most advantageous utility, however, the fibers of Layer A are synthetic, crimped, organic fibers of either staple or continuous length.

Methods of making other nonwoven fabrics useful in the practice of this invention are exemplified by the teachings in the following patents incorporated herein by refera) ence. U.S. 2,723,935, Example 1; U.S. 2,910,763, Example 1; U.S. 2,978,785, Example 2; U.S. 2,357,392, Example 6, and Belgian Patents 608,644 and 608,646.

Prior to being coated with the polymer/ fiber dispersion of the present novel method, the nonwoven fabric used as Layer A has sulficient surface roughness when under tension to be visible to the unaided eye, especially when the fabric is stretched at least 30% beyond its original length or width when viewed with a bright light held near the plane of the fabrics surface so that shadows are produced by any raised or depressed areas in the surface.

Layer B of the novel product contains intercommunieating micropores and randomly dispersed staple fibers. A major proportion (over 50%), preferably about 75 to 100%, of the dispersed fibers are free of contact with one another. The weight ratio of the microporous polymeric material to the dispersed staple fibers should be about 80:20 to 97:3, preferably about 85:15 to 9525 when the fiber dimensions are in the preferred range of about 0.8 to 6 denier and about 0.1 to 0.4 inch long. Fibers having a length of about 0.01 to 0.09 inch can also be used. At the maximum fiber content it is best not to use fibers having a denier above 6 and/ or a length of over 0.4 inch; at the minimum fiber content (3%), somewhat thicker and longer fibers can be used. The softening point and initial modulus of the fibers are preferably substantially greater than those of the polymeric material from which the microporous coating is formed. Fibers having an initial modulus above 1.0 gram per denier are usually preferred.

For most applications, the thickness of Layer B should be about 5 to mils. For reasons of economy and ease of production, Layer B should be no thicker than is necessary to provide the desired degree of product smoothness and durability. The pores in Layer B should be substantially independent of the fibers with respect to shape and location; that is, the relationship of pores and fibers should not be as described in the product of U.S. Patent 2,757,100.

Any one or more of a wide variety of synthetic or natural staple fibers can be used as the dispersed fiber component. Among the more desirable ones are nylon, rayon, acetate, acrylic and polyester fibers. In the case of synthetic fibers, staple fibers can be formed by chopping continuous filaments into relatively short or staple lengths.

The flexible (non-rigid) non-fibrous polymeric material of Layer B can consist entirely of polymer or blends thereof with such additives as curatives, color ng agents, plasticizers, stabilizers and fillers. A polymeric material is selected having properties suited to the intended application, such as flexibility, cold flow resistance, hardness and toughness. A large number of polymers, either individually or in combination, can be used, for example, polyurethane polymers, vinyl halide polymers, polyamides, alkyl esters of acrylic and methacrylic acids, chlorosulfonated polyethylene, and copolymers of butadiene and acrylonitrile. A polymeric material having an initial modulus below 1.0 gram per denier is usually preferred, especially one that is elastomeric.

Best results are obtained when the pores in Layer B are independent of the fibers with respect to shape and location. For example, in practicing the process of this invention, the flexible polymeric material and staple fibers are dispersed in a liquid which is a solvent for the polymer and a non-solvent for the fibers. Enough polymer solvent is used to yield a dispersion having a solids content and viscosity that is satisfactory for the coating process selected. The solvent used in the dispersion should be one that is miscible, preferably completed miscible, with the nonsolvent liquid to be used in practicing the invention. N,N-dimethyl formamide is a highly useful solvent for the polymers soluble therein in view of its high solvent power for many of the preferred polymers as well as its high miscibility with the generally preferred non-solvent 4- liquids including water. Other useful solvents include dimethyl sulfoxide, tetrahydrofuran, tetramethyl urea, N,N-dimethyl acct-amide, N-methyl-Z-pyrrolidone, ethyl acetate, dioxane, toluene, phenol, chloroform, gammabutyrolactone and a glycol ether of the formula Also useful are blends of these solvents with various water-miscible liquids, such as ketones and alcohols which .alone are often poor solvents for the polymer. One very useful blend is composed of dimethyl formamide and methyl ethyl ketone.

When the solvent is to be removed from the applied layer merely by drying, it should be more volatile than the non-solvent used in the process so that some nonsolvent will still be present in the layer after the solvent has been removed.

An extremely useful polymeric component is a polyurethane elastomer. Particularly preferred is a polyurethane elastomer made by reacting an organic diisocyanate with an active hydrogen containing polymeric material such as a polyalkyleneether glycoly or a hydroxy-terminated polyester to produce an isocyanate-terminated polyurethane prepolymer, and reacting the resulting prepolymer with a chain-extending compound such as water or a compound having two active hydrogen atoms bonded to amino-nitrogen atoms. Useful polyurethane elastomers can also be made by replacing all or part of the polymeric glycol with a simple nonpolymeric glycol (e.g., ethylene glycol or propylene glycol). Hydrazine and N-methyl-bis-amino-propylamine are preferred amino nitrogen containing chain extenders; however, others which are useful include dimethyl-piperazine, 4-methyl-m-phenylene diamine, rn-phenylene-diamine, 1,4-diaminopiper-azine, ethylene diamine and mixtures thereof.

The polyurethane elastomer can be prepared by first mixing a molar excess of the diisocyanate with the active hydrogen containing polymeric material and heating the mixture at about 50-120 C. until the prepolymer is formed. Or, the dissocyanate can be reacted with a molar excess of the active hydrogen containing polymeric material, and the reaction product capped by reacting it with more dissocyanate to form the prepolymer.

Aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used in forming the prepolymer. Such diisocyanates are, for example, tolylene-2,4- diisocyanate; tolylene-2,6-dissocyanate; m-phenylene diisocyanate; biphenylene 4,4'-diisocyanate; methylene bis- (4-phenyl isocyanate); 4-chloro-1,3-phenylene dissocyanate; naphthalene-1,S-diisocyanate; tetramethyleue-1,4- diisocyanate; hexamethylene 1,6 diisocyanate; decamethylene 1,10 diisocyanate; cyclohexylene-1,4-dissocyanate; methylene bis(4-cyclohexyl isocyanate) and tetrahydronaphthalene diisocyanate. Arylene diisocyanates, that is isocyanates in which the isocyanate groups are attached to an aromatic ring are preferred. In general, they react more readily than do allkylene diisocyanates.

A polyalkyleneether glycol is the preferred active hydrogen containing polymeric material for the prepolymer formation. The most useful polyglcols have a molecular weight of 300 to 5000, preferably 400 to 2000, and include, for example, polyethyleneether glycol, polypropyleneether glycol, polytetramethyleneether glycol, polyhexamethyleneether glycol, polyactamethyleneether glycol, polynonamethyleneether glycol, polydecamethyleneether glycol, polydodecamethyleneether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain such as, for example, the compound HO(CH OC H O),,H wherein n is an integer greater than 1 can also be used.

Polyesters which can be used instead of or in conjunction with the polyalkyleneether glycols are, for example, those formed by reacting acids, esters or acid halides with glycols. Suit-able glycols are polymethylene glycols, such as ethylene, propylene-, tetramethylene-, decamethylene glycol, substituted polymethylene glycols such as 2,2-dirnethyl-1,3-propanediol, cyclic glycols such as cyclohexanediol and aromatic glycols such as xylylene glycol. Aliphatic glycols are generally perferred when maximum product flexibility is desired. These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester forming derivatives thereof to produce relatively low molecular weight polymers, preferably having a melting point of less than about 70 C., and molecular weights like those indicated for the polyalkyleneether glycols. Acids for preparing such polyesters are, for example, succinic, adipic, suberic, sebacic, terephthalic and hexahydroterephthalic acids and the alkyl and halogen substituted derivatives of these acids.

The chain extension reaction is usually carried out at a temperature below 120 C. and often at about room temperature, particularly for hydrazine-extended polymers. During the reaction, prepolymer molecules are joined together into a substantially linear polyurethane polymer, the molecular weight of which is usually at least 5000 and sometimes as high as 300,000. The reaction can be carried out without a solvent in heavy duty mixing equipment or it can be carried out in a homogeneous solution. In the latter case, it is convenient to use as a solvent one of the organic solvents to be employed in the polymer dispersion.

Since the resulting polyurethane polymer has rubberlike elasticity, it is referred to as an elastomer, although the degree of elasticity and rubber-like resilience may vary widely from product to product depending on the chemical structure of the polymer and the materials in combination with it.

A vinyl chloride polymer is another preferred component of the dispersion used in forming Layer B. Superior product abrasion resistance is obtainable when a vinyl chloride polymer is used in combination with an elastomer such as the polyurethane described above. When making a flexible shoe upper material or the like from a blend of polyurethane elastomer and vinyl chloride polymer, it is often preferred to empoly a major proportion (over 50 weight percent) of the former and a minor proportion (less than 50 weight percent) of the latter. However, good leather-like products are also obtainable in accordance with this invention when the polymeric component contains a major proportion (at least 51% by weight) of vinyl chloride polymer, especially when used in combination with a plasticizer for the polymer or in combination with a minor proportion of polyurethane elastomer.

Useful vinyl chloride polymers include polyvinyl chloride and copolymers of a major proportion, preferably at least 80%, of vinyl chloride and a minor proportion of another ethylenically unsaturated monomer, such as vinyl acetate, vinylidene chloride, or diethyl maleate.

The nonwoven fabric is coated on one or both surfaces with a layer of the dispersion of flexible polymeric material and staple fibers, and the coating is converted to a microporous structure by the coagulation, solvent removal and drying steps previously specified. The dispersion layer can be applied by means of a doctor knife, extruder or other apparatus known to be useful for applying liquid coating compositions to fibrous substrates. Some of the dispersion can be allowed to soak into or impregnate Layer A before the layer of dispersion is coa-gulated. This is an especially useful procedure when no polymeric binder has previously been introduced into the nonwoven fabric. The most useful methods known for preparing the microporous structure are taught in the following patents and pending applications, the teachings of which are incorporated herein by reference:

(a) US. Patent 3,000,757, issued on September 19, 1961;

(b) US. application Serial No. 90,815, filed on February 21, 1961, now US. Patent No. 3,100,721 and allowed on Nov. 28, 1962;

(c) Copending US. application Serial No. 148,851, filed on October 31, 196 1, and

(d) Copending US. application Serial No. 164,589, filed on January 5, 1962.

These four methods have certain similarities and certain significant differences when compared with each other. Each of them results in a microporous layer in which the micropores communicate with each other and with the surfaces. Thus, the resulting coating layer has a substantial permeability value, usually about from 1000 to 10,000 or more. Permeability value designates the degree of breathability as measured by the test described by Kanagy and Vickers in the Journal of the Leather Chemists Association, vol. 45, pp. 21l242, dated April 19, 1950.

Method (a) involves applying to a substrate a layer of a solution of polymer in a liquid solvent, coagulating the layer into a microporous structure by bathing it with a nonsolvent in vapor form, removing the solvent, and then removing the non-solvent.

Method (b) involves applying a layer of a dispersion of polymer in a liquid solvent which dispersion has been made by adding enough non-solvent to a polymer solution to convert it to a substantially colloidal dispersion or incipient gel, coagulating the layer into a microporous structure by bathing it with a non-solvent, removing the solvent, and then removing the non-solvent.

Method (0) involves applying a layer of polymeric gel which has been made by adding enough non-solvent to a polymer solution to render it separable into gel and liquid portions and separating the gel portion, coagulating the layer into a microporous structure by bathing it with a non-solvent, removing the solvent, and then removing the non-solvent.

Method (d) involves applying a layer of a solution of polymer in a liquid solvent, coagulating the layer into a microporous structure by bathing it with a 10:90 to :5 (weight ratio) solverrtmon-solvent blend, removing the solvent and then removing the non-solvent.

The four methods of applying the microporous coating just described when considered as a group may be described generically as follows: A method which comprises (a) applying to a substrate a layer of polymeric material dispersed in a liquid which is a solvent for the polymer, (b) coagulating said layer into an inter-communicating microporous structure by bathing it with a non-solvent for the polymer that is at least partially miscible with said solvent, (0) removing substantially all of the solvent from the layer, and (d removing substantially all of the non-solvent from the resulting substantially solvent-free microporous polymeric layer.

In the present method, of course, the substrate is the Layer A nonwoven fabric, and staple fibers are added to the dispersion in the required amount at any convenient point prior to the coating operation so that they become randomly dispersed throughout Layer B.

In coagulating the Layer B dispersion, the layer is bathed by being placed in contact with the non-solvent bathing liquid, for example, by sudden immersion therein, by first floating the coated material on top of a body of the bathing liquid followed by immersion therein, by subjecting the layer to a spray or a vapor of the bathing liquid, or by any combination of such bathing techniques.

Substantially all of the polymer solvent is removed from the resulting coagulated microporous layer of fibercontaining polymeric material before at least the last appreciable portion of non-solvent is removed therefrom. When the solvent is more volatile than the non-solvent, this can be done by subjecting the layer to drying conditions, for example, in an oven or similar heat zone. A preferred solvent removal method is to bathe the coagulated layer with water or another non-solvent for the polymer until the layer is substantially free of the solvent. The layer is then freed of substantially all the non-solvent remaining therein by any suitable drying method, for example, by being passed through a heat zone in which there is forced air circulation.

The composite structure resulting from coating the nonwoven fabric with the microporous polymer/fiber layer is pressed in a suitable press, for example, a fiatplaten hydraulic press or a roller-type press, until the density of the microporous layer is permanently increased to at least 0.4 gram per cubic centimeter but not until the layer becomes nonporous. The press can be provided with shims to give a fixed clearance and thereby insure the control of product density and porosity. Best results are usually obtained when the microporous layer is at an elevated temperature during this compaction step, but not at a temperature high enough to melt the staple fibers or to cause undue degradation of the polymeric material. Useful results can also often be obtained by pressing at or slightly above room temperature, increasing the pressing time and/ or pressure in proportion to the decrease in temperature. In the latter case the time and pressure required are governed to a large extent by the capacity of the polymeric material to undergo cold-flow.

It is well-known in the art of compacting polymeric materials by means of a press that temperature, pressure and dwell-time are coactive factors. If a product is obtained by the present process which has unsatisfactory smoothness, the need for an increase in at least one of these factors is indicated (assuming that Layer B is of sufficient thickness). On the other hand, if a product is obtained having little or no vapor permeability, the need for a decrease in at least one of these factors is indicated.

Some preferred embodiments of the novel product comprise a third essential layer (Layer C) in superposed adherence with Layer B in the form of a substantially fiber-free microporous vapor-permeable layer of flexible polymeric material in which the pores are inter-communicating.

Layer C can be applied by the same method and from the same polymers described above in reference to Layer B except the staple fibers are omitted from the solvent dispersion of polymer and the pressing step is not essential. It is preferred that the pores in both layers (B and C) be dominantly less than 20 microns in diameter.

The solvent dispersion of polymer from which Layer C is to be formed can be applied over Layer B subsequent to any of the steps 1 to set forth above in the broad definition of the novel method. In fact, a most effective and efiicient method comprises applying the Layer C dispersion immediately after the application of the Layer B dispersion, and carrying out steps 2 to 5 simultaneously on the two dispersion coatings.

Poromeric sheet materials are obtainable in accordance with this invention which have advantages over prior art leather-like poromeric materials as well as over natural leather for many applications.

The examples which follow are given for the purpose of illustrating the invention. All quantities shown are on a weight basis unless otherwise indicated.

Example 1 A 20% solution of polyurethane elastomer is prepared by first mixing 3343 parts of polytetramethyleneether glycol of about 1000 molecular weight with 219 parts of tolylene-2.,4-diisocyanate and heating the mixture for 3 hours at 90 C. Then 2485 parts of the resulting hydroxyl-end-group-containing dimer are mixed with 570 parts of methylene-bis(4-phenylisocyanate). This mixture is heated for one hour at 80 C. yielding a prepolymer with isocyanate end groups. The prepolymer is dissolved in 10,000 parts of N,N-dimethyl formamide (sometimes referred to simply as dimethylformamide), and the resulting solution is added slowly to a solution consisting of parts of chain extender dissolved in 1,710 parts of dimethyl formamide. The chain extender con- Sists of N-methyl-bis-aminopropylamine and hydrazine hydrate in a molar ratio of 40:60. The resulting reaction mixture is stirred at 40 C. for 30 minutes to form a polyurethane solution having a viscosity of about 115 poises and a polymer content of about 20%.

A polymer solution consisting of 10.5% polyurethane elastomer, 5.7% polyvinyl chloride and 83.8% dimethyl formamide is prepared by admixing a 12% solution in dimethyl formamide of polyvinyl chloride with a suitable amount of the 20% polyurethane solution.

The resulting polymer solution is converted to a substantially colloidal dispersion by slowly admixing 12.2 parts of a 1:4 blend of water and dimethyl formamide with parts of the polymer solution.

Staple fibers of 6/6 nylon having a length of 4; inch and a denier of 3 are thoroughly blended with the polymer dispersion in an amount such that the completed dispersion has a polymer to fiber weight ratio of 91:9.

A long piece of nonwoven fabric is passed through a conventional doctor-knife coating device where the polymer/fiber dispersion is applied to the top surface of the nonwoven fabric to a wet-film thickness sufficient to give a coating of 20 mils when dried.

The nonwoven fabric is a polyurethane elastomer impregnated fibrous mat prepared in accordance with Example 1 of U.S. Patent 3,067,483, except for minor differences (e.g., the fiber denier is 0.8 instead of 0.5). It is 39 mils thick and weighs 6.5 ounces per square yard. It is made by needle-punching and shrinking a batt of 0.8 denier retractable poly(ethylene-terephthalate) fibers followed by impregnation with about 35%, based on the batts fiber content, of a hydrazine-extended polyurethane elastomer similar to the one described in this example except the chain-extender used consists entirely of hydrazine.

The layer of polymer/fiber dispersion is coagulated into a very fine-pore inter-communicating microporous structure by floating the coated material coating-side-down on a body of cold water at 20 C. and letting it gradually sink over a period of 10 to 15 minutes, followed by leaching it in hot water at C. for 60 minutes. Substantially all of the solvent (dimethyl formamide) has now been removed from the microporous layer. Next, the coated material is dried in a 92 C. heat zone. The microporous polymer/fiber layer, which will later be compacted in a press, now has a density of 0.4 gram per cubic centimeter. Substantially all of the fibers in the coating are free of contact with one another. The softening point and initial modulus of the fibers are considerably higher than those of the microporous polymeric material.

A fiber-free microporous polymeric coating is applied over the polymer/ fiber coating by first lightly spraying the coated material with water to make it moist and then repeating the procedure described above except no staple fibers are added to the polymer dispersion and the polymer dispersion is applied in an amount sufficient to give a dry-film thickness of 5 mils.

The density of the two microporous coating layers is increased, the smoothness of the product is enhanced, and the surface is embossed with a fine grain pattern by hot pressing the coated material by means of a modified rollertype apparatus and method as described in the example of copending U.S. application Serial No. 121,996, filed on July 5, 1961, by J. Hochberg, and assigned to the assignee of the present application. In this method the coated material is passed through an extended arcuate nip formed by a rotating non-yielding metal roller and a tetrafluoroethylene-coated fabric slip sheet supported by a yielding rubber-coated fabric inflated envelope which in turn is supported by a rigid steel non-rotatable restraining shoe. The surface of the rotating roller has been engraved with a fine leather-like grain pattern. The coated material passes through the nip with the coated side in contact with the engraved metal roller, the roller having a temperature 140 C. and the air-inflated envelope in cooperation with the rigid restraining shoe forcing the coated material against the metal roller under a pressure of p.s.i.g. The nip extends half way around the metal roller. Each square inch of the coated material is in the nip for a period 75 seconds.

The microporous polymer/fiber layer now has a density of 0.7 gram per cubic centimeter and the product has a permeability value of 8000. The pores in both of the coating layers are predominantly less than microns in diameter; thus, the layers are microporous since substantially all the pores are too small to be seen by the unaided eye. The pores communicate with one another and with the surfaces of the coating.

The product of Example 1 is a smooth-surface poromeric sheet material that is useful for most of the same applications as smooth-finshed natural leather (calfskin), including shoe-uppers, upholstery, shoe insoles, handbags, garments and garment linings. It can be produced in colors by incorporating coloring agents in the coating composition, by treating it in a dye bath, by coating it with a colored coating composition of the type commonly applied to leather and poromeric shoe-uppers, or by a combination of these methods. The durability, appearance and comfort characteristics of this product are similar to those of good grades of calfskin leather.

The coated surface of the Example 1 product is surprisingly smooth whether the product is in a relaxed condition or under sufiicient tension to stretch it several percent beyond its original length.

For purposes of comparison, a poromeric sheet is prepared by repeating Example 1, except the staple fibers are omitted from the polymer dispersion that is applied first to the nonwoven fabric. The coated surface of the resulting control sample and that of the Example 1 product are both viewed at a distance of 15 inches with the unaided eye while a IOU-watt light is held near the plane of the coated surfaces and while both materials are stretched 10% beyond their original length. The Example 1 product has a much smoother appearance than the control sample.

The test is repeated on shoes made with the uppers constructed of the two different materials. Again the Example 1 product has a definitely smoother appearance both in the stretched toe and heel areas and in the relaxed side areas. "Also, the Example 1 product has a more leather-like grain break; e.g., when bent sharply upon itself with the coated side inside the fold, there are finer and more evenly spaced wrinkles inside the fold.

Example 2 A poromeric sheet material having smoothness and utility similar to the product of Example 1 is prepared by repeating Example 1 except for the omission of the fiber-free microporous coating.

Example 3 A poromeric sheet material having smoothness and utility similar to the product of Example 1 is prepared by repeating Example 1 except the nonwoven fabric used in that example is replaced with a different type of nonwoven fabric having a density of 0.45 grams per cubic centimeter. This nonwoven fabric is composed of poly (ethylene therephthalate) continuous filaments having a loop configuration, about 50 crimps per inch, and separate and random disposition within the fabric, the filaments being bonded together at spaced points throughout the fabric with cospun filaments of an 80/20 copolymer of ethylene terephthalate and ethylene isophthalate. The majority of the loops are substantially in the plane of the fabric. The weight ratio of the poly(ethylene terephthalate) filaments to the copolymer binder filaments in the fabric is 91:9. The fabric also contains a porous polyurethane elastomer impregnant.

The nonwoven fabric is prepared as follows. Using an apparatus similar to that described in Example 2 of Belgian Patent 608,646, poly(ethylene terephthalate) having a relative viscosity of 34 is melt-spun into filaments from a 68-hole spinneret (7 mil hole diameter) while the /20 ethylene terephthalate/isophthalate copolymer is cospun into filaments from an adjacent 34-hole spinneret. Nine grams of copolymer filaments are spun for each 91 grams of the former. The freshly spun filaments are passed in rubbing contact with chromic oxide guide bars to give them an induced electrical charge. An aspirating air jet operating with 50 p.s.i.g. pressure is employed to attenuate and quench the filaments, advance them to an aluminum plate receiver and lay them down on the receiver in separate and random fashion in the form of a loosely constructed nonwoven fabric or batt. The receiver is moved sufficiently to yield a batt of uniform thickness.

Next, the batt is placed between two sheets of paper in a press and consolidated into a denser and stronger nonwoven fabric under a pressure of p.s.i. while heated to 60 C. The consolidated fabric is removed from between the paper sheets, placed in the press between two pieces of 60 mesh wire screen, and embossed under a pressure of 150 p.s.i. while heated at 210 C. The latter operation completes the crimping and the bonding of the filaments. Two plies of the resulting material are laminated into a composite fabric by placing one atop the other in a heated press and pressing for 20 seconds at 154 C. at a pressure of 3 p.s.i.g. The composite fabric is then cooled to 22 C. and impregnated with about 35%, based on the weight of the unimpregnated fabric, of the same type of polyurethane elastomer employed as the impregnant in Example 1.

Example 4 Four different poromeric sheet materials having smoothness and utility almost equal to the product of Example 1 are prepared by repeating Example 1 except the polymer: fiber weight ratios in the four different dispersions first applied to the nonwoven fabric are 81:19, 86:14, 89:11 and 94:6 respectively.

Example 5 A poromeric sheet material having smoothness and utility similar to the product of Example 1 is prepared by repeating Example 1 except the fiber-free dispersion coating is applied prior to the coagulation of the fibercontaining dispersion coating, followed by bathing and drying of the composite coating in a single operation. This procedure is substantially more economical than that of Example 1.

Example 6 A poromeric sheet material having smoothness and utility similar to the product of Example 1 is prepared by repeating Example 5 except the nonwoven fabric employed as the substrate is wool felt having a thickness of 30 mils and a weight of 3.2 ounces per square yard. Also, the thickness of the polymer/fiber coating is 40 mils and that of the fiber-free coating is 10 mils immediately prior to the final hot pressing step. The product has a total thickness of 60 mils.

I claim:

1. A poromeric sheet material comprising layer A, a vapor-permeable nonwoven fabric comprised of fibers which are in entangled and interlocked relationship with one another, and

layer B, in superposed adherence with nonwoven fabric layer A, a vapor-permeable fiber-containing layer of flexible polymeric material, said layer B having (1) an inter-communicating microporous structure, (2) a density of at least 0.4 gram per cubic centimeter,

(3) staple fibers in a random state of dispersion throughout the layer, a majority of the fibers being free of contact with one another, and

(4) a polymeric material:staple fiber weight ratio of about 80:20 to 97:3.

2. An article as defined in claim 1 wherein layer A is comprised of crimped synthetic organic fibers.

3. An article as defined in claim 1 wherein layer A is a needle-punched nonwoven fabric comprised of in situretracted organic fibers, said fabric having been shrunk about to 90% of its original planar area, and dispersed throughout said fabric about 5 to 90% of a porous flexible polymeric impregnant based on the combined weight of fibers and impregnant.

4. An article as defined in claim 3 wherein said flexible polymeric material is a polyurethane elastomer.

5. An article as defined in claim 3 wherein said flexible polymeric material is a blend of polyurethane elastomer and a vinyl chloride polymer.

6. An article as defined in claim 3 wherein substantially all of the staple fibers in layer B are free of contact with one another.

7. An article as defined in claim 6 wherein the polymeric material:staple fiber weight ratio in layer B is about 85: to 95.5 and the fibers have a denier of about 0.8 to 6 and a length of about 0.1 to 0.4 inch.

8. An article as defined in claim 3 wherein a vaporpermeable fiber-free layer of microporous flexible polymeric material is in superposed adherence with layer B.

9. A method which comprises (1) applying to a nonwoven fabric as defined in claim 1 a dispersion of flexible polymeric material and staple fibers in a liquid which is solvent for the polymeric material and a non-solvent for the fibers, the polymeric material:staple fiber weight ratio being about 80:20 to 97:3,

(2) coagulating the layer applied in (1) into an intercommunicating microporous structure by bathing it with a liquid non-solvent for the polymer that is at least partially miscible with the liquid used in (1),

(3) removing substantially all of the solvent from the microporous layer,

(4) removing substantially all of the non-solvent from the resulting solvent-free microporous layer, and

(5) pressing the resulting composite structure under conditions sufficient to increase the density of the coating permanently to at least 0.4 gram per cubic centimeter, but not suflicient to render the coating nonporous.

10. A method as defined in claim 9 wherein the nonwoven fabric is as defined in claim 3, the flexible polymeric material is a blend of a polyurethane elastomer and a vinyl chloride polymer, the liquid in step (1) is dimethyl formamide, and the liquid non-solvent in step (2) is water.

11. A method as defined in claim 10 wherein the dispersion used in step (1) is prepared by adding water to 1.2 a dimethyl formarnide solution of the polymeric material until a substantially colloidal dispersion of the polymeric material is formed, and mixing staple fibers with the colloidal dispersion.

12. A method as defined in claim 11 wherein step (5) comprises pressing the composite structure for about to 90 seconds at a temperature of about 130 to 170 C. and a pressure of about 5 to 20 p.s.i.g.

13. A method of making a smooth-surface poromeric sheet material which comprises (a) forming a dimethyl formamide solution of a blend of a polyurethane elastomer and a vinyl chloride polymer,

(b) adding enough water to the resulting solution to convert it to a substantially colloidal polymeric dispersion,

(c) mixing enough staple fibers with the colloidal dispersion so that the weight ratio of polymer to fibers in the mixture is about :20 to 97:3, the softening point and initial modulus of the fibers being substantially greater than those of the polymer,

(d) applying to a nonwoven fabric as defined in claim 3 a layer of the polymer/fiber dispersion,

(e) applying to the layer applied in step (d) a layer of a fiber-free polymeric dispersion prepared by repeating steps (a) and (b),

(f) coagulating the layers applied in steps (d) and (e) into a composite inter-communicating microporous structure by bathing the coating with water,

(g) removing substantially all of the dimethyl formamide from the microporous coating by continuing to bathe the coating with water,

(h) drying the coated material in a heat zone,

(i) pressing the composite structure while a heated pressure element is in contact with the coated surface for about 60 to seconds at a temperature of about to C. and a pressure of about 5 to 20 p.s.i.g., thereby increasing the density of the polymer/ fiber layer applied in step (d) to at least 0.4 gram per cubic centimeter, and

(j) cooling the coated material to room temperature.

14. A method as defined in claim 13 wherein the staple fibers added in step (e) have a denier of about 0.8 to 6 and a length of about 0.1 to 0.4 inch.

References Cited by the Examiner UNITED STATES PATENTS 25,192 8/1859 Goodyear 117-135.5 2,490,001 11/1949 Jayne et al. 26077 2,751,363 6/1956 Martin 26040 XR 3,067,482 12/1962 Hollowell 1l763 XR 3,067,483 12/1962 HolloWell 117-140 3,100,721 8/1963 Holden l17135 WILLIAM D. MARTIN, Primary Examiner. 

1. A POROMERIC SHEET COMPRISING LAYER A, A VAPOR-PERMEABLE NONWOVEN FABRIC COMPRISED OF FIBERS WHICH ARE IN ENTANGLED AND INTERLOCKED RELATIONSHIP WITH ONE ANOTHER, AND LAYER B, IN SUPERPOSED ADHERENCE WITH NONWOVEN FABRIC LAYER A, A VAPOR-PERMEABLE FIBER-CONTAINING LAYER OF FLEXIBLE POLYMERIC MATERIAL, SAID LAYER B HAVING (1) AN INTER-COMMINICATING MICROPOROUS STRUCTURE, (2) A DENSITY OF AT LEAST 0.4 GRAM PER CUBIC CENTIMETER, (3) STAPLE FIBERS IN A RANDOM STATE OF DISPERSION THROUGHOUT THE LAYER, A MAJORITY OF THE FIBERS BEING FREE OF CONTACT WITH ONE ANOTHER, AND (4) A POLYMERIC MATERIAL:STAPLE FIBER WEIGHT RATIO OF ABOUT 80:20 TO 97:3.
 9. A METHOD WHICH COMPRISES (1) APPLYING TO A NONWOVEN FABRIC AS DEFINED IN CLAIM 1 A DISPERSION OF FLEXIBLE POLYMERIC MATERIAL AND STAPLE FIBERS IN A LIQUID WHICH IS SOLVENT FOR THE POLYMERIC MATERIAL AND A NON-SOLVENT FOR THE FIBERS, THE POLYMERIC MATERIAL:STAPLE FIBER WEIGHT RATIO BEING ABOUT 80:20 TO 97:3, (2) COAGULATING THE LAYER APPLIED IN (1) INTO AN INTERCOMMUNICATING MICROPOROUS STRUCTURE BY BATHING IT WITH A LIQUID NON-SOLVENT FOR THE POLYMER THAT IS AT LEAST PARTIALLY MISCIBLE WITH THE LIQUID USED IN (1), (3) REMOVING SUBSTANTIALLY ALL OF THE SOLVENT FROM THE MICROPOROUS LAYER, (4) REMOVING SUBSTANTIALLY OF THE NON-SOLVENT FROM THE RESULTING SOLVENT-FREE MICROPOROUS LAYER, AND (5) PRESSING THE RESULTING COMPOSITE STRUCTURE UNDER CONDITIONS SUFFICIENT TO INCREASE THE DENSITY OF THE COATING PERMANENTLY TO AT LEAST 0.4 GRAM PER CUBIC CENTIMETER, BUT NOT SUFFICIENT TO RENDER THE COATING NONPOROUS. 